Stem cells are cells having both properties of multipotent potential of producing cells that are differentiated into a plurality of cells, and self-replicating potential of producing identical cells by cell division. Stem cells derived from an embryo, an early developmental stage of a fertilized egg, are embryonic stem cells (ES cells). Human ES cells are expected to be applied to regenerative medicine, but due to ethical concerns associated with the use of fertilized eggs, the creation of new ES cells is not permitted.
In recent years, as cells having properties similar to embryonic stem cells, attention has also been focused on artificially induced pluripotent stem cells (iPS cells). However, the creation of iPS cells is associated with various problems such as cancerous changes in cells and poor efficiency of generating the cells. On the other hand, somatic stem cells having capable of differentiating into a specific tissue have no such ethical problems, unlike embryonic stem cells, since they are derived from a patient's own tissue, such as bone marrow.
It is well known that, in the skin, there are epidermal stem cells in the epidermal basal layer (Non-patent document 1) and it is reported that there are follicular epithelial stem cells (Non-patent document 2) and cutaneous melanocyte stem cells (Non-patent document 3) in a region referred to as the hair follicle bulge area. On the other hand, in the dermis, thin spindle-shaped fibroblasts are present in the fiber component comprising collagen as the main ingredient, but it has not been demonstrated whether stem cells are present in the dermal fibroblasts. It is also known that in the dermis there are skin-derived precursor cells (SKP) that differentiate into a plurality of cell lineages such as adipocytes, glia cells, chondrocytes and myocytes (Non-patent document 4), but no relationship has been confirmed between dermal fibroblasts and SKP.
Mesenchymal stem cells isolated from bone marrow as precursor cells of fibroblasts (Non-patent document 5) can differentiate into various cells (osteocytes, myocytes, chondrocytes, adipocytes, etc.) belonging to the mesenchymal system, and thus are expected to be applied to regenerative medicine, such as reconstruction of bones, blood vessels and muscles. Recently, evidence is growing showing the likelihood that mesenchymal stem cells may occur in many tissues having mesenchymal tissue, and mesenchymal stem cells have also been isolated from fat, cord blood, placenta, etc. (Non-patent documents 6 to 8). However, the presence of mesenchymal stem cells in the dermis has not been shown yet.